1. Field of the Invention
The invention relates generally to the field of carbon containing tips. More particularly, the invention relates to carbon containing tips that can be used as field emitting devices.
2. Discussion of the Related Art
For many years, thermionic vacuum tubes were the dominant devices in electronic circuits and systems. However, vacuum tube technology was almost completely replaced by semiconductor technology in the late 1950s due to four major disadvantages associated with vacuum tube technology. First, power was consumed to heat the electron source to cause thermionic electron emission. Second, high operational voltages were required. Third, current densities were extremely low (xcx9c0.5 A/cm2). Fourth, high levels of integration (e.g. integrated circuits) could not be reached.
Although it has been more than 40 years since the decline of the vacuum tube, strong interest and active research has recently reemerged in vacuum microelectronics (Brodie and Schwoebel, 1994; Temple, 1999). A practical vacuum microelectronic technology has been pursued to achieve the following advantages. First, is the advantage of high-frequency operation. Ballistic transport of electrons in a vacuum is inherently faster than collision-limited transport in a solid. Operation at THz frequencies and above may be possible. Second is the advantage of temperature insensitivity: Devices based on field emission would operate over a very large temperature range compared to semiconductor devices. Third is the advantage of radiation hardness. Vacuum devices are inherently radiation hard since they do not depend on transport through a low-defect lattice. Fourth is the advantage of being able to utilize simple materials; No high-purity, single crystal materials are required. Fifth is the advantage of small size and high-density integration: Individual VME devices can become substantially sub-micron in size, leading to device densities  greater than 108/cm2, in striking contrast to the limitations of vacuum tubes.
The renewed interest in vacuum microelectronics was fueled by Spindt""s development of a field emission tip (now known as the Spindt tip) that operates at pressures easily accessible for practical devices and manufacturable by modem microfabrication techniques (Spindt, 1968). Spindt Tips are metallic cones with a tip radius of curvature of xcx9c300 xc3x85 that allows for a large geometrical enhancement of the local electric field and a relatively low turn-on voltage (Brodie and Schwoebel, 1994). FIG. 1 shows a microfabricated field-emission element Spindt Tip 100.
However, Spindt-tip emitters have not achieved widespread use in vacuum microelectronics, for several reasons. First, they must be lithographically defined and consequently are expensive to fabricate in large arrays. Second, metallic emitters (or metal-coated Spindt tips) now are recognized as intrinsically unstable. High-mass residual gases sputter-etch metallic emitters, while light gases (H2, He) cause sputter-assisted atomic diffusion that, in the high local electric field, results in growth of nanoscale protrusions (Dyke and Dolan, 1956; Cavaille and Dechster, 1978). The protrusions in turn cause increased emission current and still more rapid protrusion growth, leading to uncontrolled emission and destruction of the emitter by a vacuum arc (Dean and Chalamala, 1999). (The effect of this intrinsic instability can be reduced by placing a series resistance in the emitter circuit (Ghis et al., 1991), to introduce negative feedback and extrinsic stability that extends lifetime.)
Electron emitters are required for a number of devices including vacuum tubes, displays, and electron lithography systems. Electrons can be extracted from an emitter by heating the emitter to a high temperature (thermal emission). However, there are many disadvantages to thermal emission. First, power is required to heat the emitter. Second, current density is low. Third, emission current is sensitive to changes in ambient temperature. Because of the high work function of electron emitter material, thermal electron emitters are used in most devices. However, stable, reproducible, mass producible field emitters would be preferred.
Recently a nanoscale field emission tube (i.e. a xe2x80x9cnanotriodexe2x80x9d) that used metal nanopillars as field emitters was reported (Driskill-Smith and Hasko, 1999; Driskill-Smith et al., 1997). This device represents a significant step forward since it demonstrates a nanoscale electronic device that could in principle be scaled to packing densities as high as 1010 devices/cm2 (Driskill-Smith and Hasko, 1999; Driskill-Smith et al., 1997). However, metal nanopillars fabricated in this way are only marginal field emitters, for several reasons. Through small in diameter they are not sharpened, so they have a low aspect ratio (AR=height/tip diameter) and consequently a low geometrical enhancement factor, GEF, for the local electric field. In addition, the resulting threshold field strength for significant nanopillar emission is quite high (estimated  greater than 150 V/xcexcm from the data in Driskill-Smith and Hasko, 1999 and Driskill-Smith et al., 1997 and very close to the breakdown field of the nearby dielectric (Spindt, 1968). The nanopillars are difficult to fabricate reproducibly (there may be one or several nanopillars in each emitter well, they are not centered, and probably only the tallest nanopillar emits current).
Heretofore, the requirements of a field emitters that do not need to be lithographically defined, are non-metallic, have a high aspect ratio and consequently a high geometrical enhancement factor, have a low threshold field strength, and are relatively easy to fabricate referred to above have not been fully met. What is needed is a solution that addresses all of these requirements.
There is a need for the following embodiments. Of course, the invention is not limited to these embodiments.
One embodiment of the invention is based on a method, comprising: providing a substrate; depositing a catalyst, said catalyst coupled to said substrate; depositing a dielectric layer, said dielectric layer coupled to said substrate; depositing an extractor layer, said extractor layer coupled to said dielectric layer; forming an extractor aperture in said extractor layer; forming a dielectric well in said dielectric layer to expose at least a portion of said catalyst; and then fabricating a carbon containing tip i) having a base located substantially at said bottom of said dielectric well and ii) extending substantially away from said substrate. Another embodiment of the invention is based on an apparatus, comprising: a substrate; an electrode structure coupled to said substrate, said electrode structure including a dielectric layer coupled to said substrate, said dielectric layer including a dielectric well that is formed in said dielectric layer after said dielectric layer is deposited; and an extractor layer coupled to said dielectric layer, said extractor layer including an extractor aperture; and a carbon containing tip coupled to said substrate, said carbon containing tip having a base located substantially at a bottom of said dielectric well and extending substantially away from said substrate, said carbon containing tip being grown from the bottom of said dielectric well using a catalyst that is introduced at said bottom of said dielectric well after said dielectric well is formed. Another embodiment of the invention is based on a method comprising: providing a substrate on a heater plate in a vacuum chamber; providing a carbon source gas and an etchant gas; heating said substrate with said heater plate; and then fabricating a carbon containing tip on said substrate with said carbon source gas and said etchant gas using plasma enhanced chemical vapor deposition.
These, and other, embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating various embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions and/or rearrangements may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such substitutions, modifications, additions and/or rearrangements.